An elevator car is driven in an elevator hoistway with an electric motor in response to the elevator calls given. The speed of an elevator car starting to move is accelerated evenly to maximum speed, and the speed is decelerated again evenly to zero when the elevator car arrives at a stopping floor.
The speed of an elevator car is usually measured with an encoder from the end of the shaft of the rotor of the electric motor, and the measured speed is adjusted to be that desired by adjusting the current of the electric motor with a frequency converter.
If the encoder fails or if operation of the encoder is interrupted, e.g. during an electricity outage, the operation of the elevator is also interrupted. Use of an elevator during installation also requires installation of an encoder or corresponding motion sensor on the electric motor.